The present invention relates to chemically amplified resist including an alicyclic acrylic polymer and a photoacid generator, and added resin having an aromatic ring, which is usable as positive resist, for example, to be applied to pattern formation wherein the positive resist is formed on a semiconductor substrate, exposed to ArF excimer laser light projected through a mask or a reticle, processed with PEB (Post Exposure Bake), and developed with a developer.
In conventional photolithography technique, a solubility-suppressed positive resist wherein a novolac polymer is used as a base polymer with added naphthoquinonediazido as a photosensitive is exposed to g-ray (436 nm) or i-ray (365 nm). However, lithography applying far ultraviolet rays such as excimer laser light of 248 nm or 193 nm has become required along with progress of fine integration of semiconductor circuits. As for the excimer laser light, the above conventional resist is not convenient because of its too strong photo-absorption to obtain a good resist pattern together with its too amplified photosensitivity. Hence, the chemically amplified(l resist making use of an acid catalyst obtained from a photoacid generator (hereafter abbreviated as PAG) is proposed as a resist material for the short-wave lithography or the electron beam lithography requiring high sensitivity.
However, problem of the photo-absorption is serious for resist material to be applied to ArF excimer laser lithography of 193 nm exposure light, and so, components of the resist material are severely restricted. As to chemically amplified resist for ArF excimer laser, there has been proposed two-component positive resist consisting of alicyclic acrylic polymer, having no problem of the photo-absorption, and a PAG, (for example, by Nakano et al., in a paper "Positive Chemically Amplified Resist for ArF Excimer Laser Lithography Composed of a Novel Transparent Photoacid Generator and an Acrylic Terpolymer", in Proceedings of the Society of Photo-optical Instrumentation Engineers, vol. 2438, pp. 433-444). However, this two-component positive resist was not practical because of its low thermal stability and very poor resistance against dry-etching to be performed for etching a base film according to a resist pattern developed thereon.
As for resist material having improved thermal stability and resistance against dry-etching, chemically amplified resist consisting of a phenolic polymer and a PAG and further including a crossing agent is proposed in a Japanese patent application laid open as a Provisional Publication No. 323610/'93. However, with this resist material having strong photo-absorption to ArF excimer laser, rectangle cross section of the resist pattern cannot be obtained and a resist pattern 202 developed on a wafer 201 becomes tapered, as schematically illustrated in FIG. 2. This tapered resist pattern is fatal especially for fine pattern configuration, degrading resolution, focusing and size accuracy.